1. Description of the Invention
The invention relates to a lifting hook wherein a control line is connected by means of a resilient and smooth connecting piece to the end of the hook point.
A lifting hook that is suspended from a crane is widely used for lifting loads. If the load is provided with a fixed lifting eye, the lifting hook is inserted therein. Usually, however, a load is not provided with a lifting eye and one or more short lines or chains, so-called lifting slings, are used to fix the load to the lifting hook. In this case the lifting sling(s) can be linked together on one lifting eye which is placed in the lifting hook, or the lifting sling(s) can be individually placed in the lifting hook. In a number of cases the hook opening is provided with a locking system to prevent undesirable slipping in and out.
For a large proportion of the loads the lifting eye or the lifting sling(s) is/are fitted into the hook opening manually by one or more persons. The locking system, if fitted, is then closed, also manually or automatically, and the crane lifts the load on the hook. Unhooking again takes place manually in the reverse sequence.
Strength and dexterity on the part of the operator are required both for hooking up and for unhooking. In addition, during these operations the operator can be injured, which can occur in diverse ways, for example by limbs becoming trapped, by movements of the hook and the load and by movements of the working platform on which the operator is located.
These problems arise especially in situations where external forces and movements act on the hook, the load, the operator and the working platform. Manual hooking up and unhooking are both made more difficult as a result. This arises, for example, on board ships which are unloading cargo at a (fixed) offshore platform at sea. Because of these risks the operator will usually wait for a suitable moment to hook up or unhook.
In addition, there are also situations where it is difficult or impossible to allow this connection to be made by a person because there is no suitable or safe place for the person. Consequently, the field of application for lifting loads is restricted.
A number of solutions already exist for lifting loads to and from a level far below the working level, which solutions are aimed at lifting pumps and turbines under a liquid level. These applications are directed in particular towards hooking up and make use of a vertical guide line which has been fitted beforehand and which is permanently connected to the load. In contrast to the present invention, an individual guide line is needed for each load.
An example of this is described in EP 0 661 232 A1 (94 85 0232) for lifting a load such as a submersion pump or turbine from a level far below the working level. In this case use is made of a permanently installed guide line permanently connected to the load. Said line must be made of material that does not corrode, e.g. nylon, and must be so thin that no one would consider using it to lift the load. The guide line runs from the point of the hook through the lifting eye on the pump and vertically up again via two guides on the hook.
The patent does describe a line on the hook point but has the following two differences compared with the present invention:
1) The patent describes a slack line with minimal lifting strength with, as an example, nylon as the material. Based on material data for nylon, a line 6 mm in diameter offers a breaking strain of 750 kgf and a line 8 mm in diameter offers a breaking strain of 2080 kgf. The description xe2x80x98that no one would consider using it to lift a loadxe2x80x99 indicates a line less than 6 mm in diameter. Based on material data for nylon, a solid circular rod 6 mm in diameter offers flexural resilience (E.I) of 0.15 N.m2. Compared with a solid rod, a plaited rope has a resilience of the order of 5-10%: 0.01 N.m2.
2) In the figures the patent shows a slack connection between the line and the hook point, as can be seen in FIG. 1 and FIG. 2. In FIG. 1 the angle between the line (12, 13) and the hook point (11) is approximately 50 degrees and in FIG. 2 said angle is approximately 0 degrees. The tensile stress in said thin and slack line between the guide(s) and the hook point is essential for guiding the lifting eye into the hook. Without tensile stress, the slack line will not hook the hook point into the lifting eye.
In addition, the system operates only by allowing a line to run vertically downwards from the hook point to the lifting eye and vertically up again to the guides and, from the latter, up to the working floor which is at a higher level. With this arrangement the lifting eye is lifted and hooked up between these two points. This embodiment is therefore usable only for lifting loads far below the working level. The system described does not function for loads which are at the same height as the working level. The specific connecting piece between the line and the hook point of the present invention is, nevertheless, not described.
The aim is achieved by means of a hook system as described above having the characterizing features discussed below.
The control line can be made of any materials known from the prior art and can comprise either a line, chain or flexible material.
The connecting piece can be made of any materials known from the prior art and can comprise a line, hinged material or flexible material. A connecting piece of short length suffices for the majority of applications, but for a number of applications the connecting piece can also have a length such that a control line is no longer needed.
The resilience of the connecting piece is necessary in order to be able to position the lifting eye well in front of the hook point, both in three coordinates and three rotations. With a slack line the lifting eye will not position well in front of the hook point, as a result of which hooking up is made more difficult.
In addition, the resilience is needed for lifting loads to and from a level at the same height as or above the working level; in this case the lifting eye is lifted, sliding along the line, into the lifting hook. In the case of a slack line the lifting eye will not be lifted up but will remain stuck in front of the hook point.
The resilience of the connecting piece can be constant over the length of the connecting piece but can also decrease from the hook point end to the control line end. For good positioning of the lifting eye in front of the hook point it is necessary for that part of the connecting piece at the hook point end to be resilient; a transition between the slack control line and the rigid hook point is achieved in this way. The resilience of the section of the connecting piece at the control line end can be minimal; the control line itself does not have to have any resilience.
A steel rope with a length of the order of 1 m and a diameter of 10 mm suffices as a connecting piece for a typical lifting hook with a lifting capacity of 75 tonnes BL (failure load) and a weight of 15 kg. This rope corresponds to a minimum resilience expressed as modulus of elasticity multiplied by moment of inertia (E.I) of the order of 0.5 N.m2. The system still functions with half this resilience, but under dynamic loading the lifting eye will hook up less frequently.
The following expression for the resilience of the connecting piece at the hook point is proposed as the lower limit for proper functioning:
EIxe2x88x92(BL{circumflex over ( )}3)/1500000+0.01
where
{circumflex over ( )}3=raise to the power of three
E=modulus of elasticity in (N.mxe2x88x922)
I=moment of inertia (m4)
BL=break load at which hook gives way in (tonf).
The hook shape and hook point can be of any shapes known from the prior art.
In the case of a hook point having a component directed upwards, the lifting eye and/or the lifting sling(s) remain(s) in the hook under the action of gravity; with this arrangement it is possible for a locking mechanism to be fitted. An additional release mechanism is needed for detaching the hook.
In the case of a hook point having a component directed downwards, a locking mechanism or a sunken rim is needed to hold the lifting eye and/or the lifting sling(s) in the hook against the action of gravity. In the case of a locking mechanism, the hook releases on opening the locking mechanism.
According to an advantageous embodiment, the control line is also used to operate the locking mechanism or release mechanism. In this context three embodiments are possible when using a single connecting line:
1) A transverse (sideways) stroke by the control line is used to operate the mechanism. This operation can comprise any systems known from the prior art. According to an advantageous embodiment, a rotary or bending construction is fitted between the hook body and the hook point with the connecting piece and the control line. Turning of the hook point by said xe2x80x98strokexe2x80x99 triggers the release/locking mechanism, as a result of which the lifting eye and/or lifting sling(s) is/are able to unhook.
2) An axial constant loading is used to operate the mechanism. This operation can comprise any systems known from the prior art. According to an advantageous embodiment, the control line is connected by means of the connecting piece to a pivoting dog, which rotates as a result of the tensile force of the control line and triggers the release/locking mechanism.
3) An axial jerk on the control line is used to operate the mechanism. This operation can comprise any system known from the prior art. According to an advantageous embodiment, the control line is connected by means of the connecting piece to a pivoting dog, which rotates as a result of the axial jerk on the line and triggers the release/locking mechanism.
In addition, there are also a number of possibilities for multiple control lines, it being possible for the above possibilities for the single control line to be combined. A particular embodiment of this is an inner line and an outer line, a so-called xe2x80x98Bowdenxe2x80x99 line. By this means it is possible to exert not only tensile force but also compressive force by means o; the inner line. This embodiment is outstandingly suitable for implementation of a highly reliable operation of the release/locking mechanism, which operation takes place only by means of, for example, a combination of tensile force on the outer line and compressive force on the inner line. The likelihood of this combination of interplay of forces in response to external forces is slight.
According to a further advantageous embodiment, a rope loop is fitted through the lifting eye and/or the lifting sling(s) beforehand. This rope loop is then connected to the control line at the hook point and, by pulling round the rope loop, the control line is guided through the lifting eye and/or lifting sling(s). This embodiment makes it possible for a person to be able to feed the control line through the lifting eye and/or lifting sling(s) even from some distance away.
According to a further advantageous embodiment, the hook construction is such that the release/locking mechanism cannot be operated when the hook is under load.